The 58-year-old bridge had a “fracture critical” design, meaning loss of a single structural support could undermine the crossing.

That is what appears to have happened. A freight truck carrying an oversized load of drilling equipment hit several overhead trusses, according to the National Transportation Safety Board.

The Skagit River bridge had been assessed as structurally sound after being hit by a vehicle in November and an inspection in January. Its design is out-of-date, but it was not unsafe until its trusses were shredded that it folded like an accordion.

Those facts, however, should not obscure a larger problem with Washington’s aging infrastructure, and the need for a booster shot to the state’s road-maintenance budget.

Of the state bridges, 135 are rated as “structurally deficient” — requiring significant work to keep them safe — including 10 on I-5 or I-90 in King County alone, according to the state Department of Transportation. In the Seattle-Tacoma-Bellevue metro area, an estimated 16 drivers cross a structurally deficient bridge every second. The American Society for Civil Engineers recently gave Washington a C-minus for bridge maintenance.

Washington made gains in the 1990s, reducing the number of structurally deficient bridges, but backslid in the 2000s, according to an analysis by the libertarian Reason Foundation.

The Great Recession contributed to a disinvestment in infrastructure, but political leaders are also susceptible to winking at sexy new projects while neglecting the duty of upkeep.

Such tendencies are on display

in the state Legislature, which is considering an $8.4 billion transportation revenue proposal paid for mostly with a 10-cent-per-gallon gas-tax increase. Just $900 million of the package is dedicated to maintenance, and a good chunk of that would go to stormwater-mitigation projects, not road or bridge replacement.

The Skagit River bridge — despite the fact it was a functional, if old, bridge before the collision — will add political pressure to pass a package this year, which is good. But the plan, proposed by House Democrats, is too top-heavy with new projects.

That is a recipe for future bridge collapses. And next time, we may not escape with solely economic losses.